A disadvantage of some containers intended for microwave heating is that, during exposure to electromagnetic radiation in the oven cavity, certain food products are subject to nonuniform heating wherein hot spots form scorched and hardened areas of food product. It is generally desirable that the container enable substantially uniform heating of the food product for a predetermined length of time in the microwave oven without damaging the food product.
The present invention pertains to a container suitable for microwave heating of cheese sauces and for heating of other viscous liquid food substances as well.
The term "cheese sauce" herein refers to pasteurized process cheese spread, as defined at 21 CFR .sctn..sctn.133.169-180, and to other flowable products which contain cheese.
Pasteurized process cheese spread typically contains natural cheese and an emulsifying agent such as a salt, and may contain dairy ingredients such as cream, milk, skim milk, whey, or any of these dairy ingredients from which part of the water has been removed (e.g., concentrated skim milk). Pasteurized process cheese spread may have a moisture level as high as 60%. Other cheese sauces may have higher moisture levels.
Cheese sauces are among the products that have been found to be susceptible to scorching during microwave heating. Where the cheese sauce is intended to be dispensed as a liquid after being heated, such scorching is, of course, entirely unacceptable. This is particularly true where the cheese sauce is packaged in a squeeze bottle for dispensing through a small opening and scorched portions may obstruct flow.
As is known in the art, despite efforts to provide relative uniformity of field intensity in the oven cavity through the use of mode stirrers, field intensity often varies widely as a function of location in the oven cavity. In the past, much effort has been directed toward controlling exposure of the food product to electromagnetic radiation in the oven cavity. Various shields, reflectors, and/or susceptors have been used to enable acceptable temperature gradients to be maintained for certain food products.
However, such devices add to the cost of the package and, in the case of shielding, tend to reduce the rate of heating of the food product, thus increasing the time required to bring the food product to a desired temperature. Such devices generally are useful principally for heating of non-homogeneous food products to enable particular temperature and heat transfer parameters to be maintained.
There is a need for a disposable container for microwave heating of cheese sauce that is suitable for commercial retail sale. In addition to enabling relatively uniform heating of the contents without scorching, the container must satisfy additional requirements, one of which is that the container must not unduly retard heating of the food product. Other considerations include the ability of the container to receive product in filling operations; the ability of the container to withstand various loads during filling, sealing, shipping, display and consumer use; the ability of the container to be packed efficiently among like containers; the appearance of the container, i.e., whether it is sufficiently attractive to be suitable for retail display; biodegradability and/or recyclability; and cost.
A general object of the invention is to provide a container designed to permit uniform heating of a food product such as a viscous cheese sauce at an acceptable rate by exposing the cheese sauce and container to electromagnetic radiation in a microwave oven.
A further object is to provide a lightweight, economical plastic container suitable for packaging of viscous products for retail sale.